#!/usr/bin/python
# -*- coding: utf-8 -*-
n=input()


li=map(int,raw_input().split())
li.sort()
tmp=li[1]-li[0]
fg=0
if n==2:
    print "Possible"
else:
    for i in range(1,len(li)-1):
        if tmp!=li[i+1]-li[i]:
            fg=+1
            print "Impossible"
            break
        else:
            continue
    if fg==0:
        print "Possible"